8 



Woody 11. In the case of most trees 



Boots. the old roots become hard and woody as they thicken and 

 then they no longer absorb water and food materials from 

 the soil but merely serve as conducting pipes to pass on 

 to the stem the supplies which have been collected by the 

 younger roots. They also anchor the tree more strongly in 

 the ground, the massive roots resisting the lever-like strains 

 exerted by the heavy trunk with its great crown of foliage, 

 as it sways in the wind. In the case of many Indian trees the 

 roots form woody supports, like buttresses, at the base of the 

 trunk, which are for instance very characteristic of Bombax 

 malabaricum, see Fig. 4 } Plate XL 



Subterra- 12. According as roots are 



nean developed in the earth, water, or air, they may be called 



JSdai Roots, subterranean, aquatic or cerial. The aerial roots of the 

 Banyan on reaching the soil, branch and develop a vigorous 

 root-system therein, while the aerial portions become woody 

 and support the horizontal branches like columns. In Rubus 

 lasiocarpus, the serial roots produced at the tips of the long 

 curved branches give rise to young plants, which become inde- 

 pendent and are separated from the parent by the decay of the 

 connecting branches. 



Other aerial roots serve as attachment organs and enable 

 climbing stems to cling firmly to their substratum ; these are 

 iound in the Ivy, Ficus scandens, and many others. These 

 roots are also in some cases able to absorb moisture and food 

 materials, provided that such are available. Thus some climbing 

 stems are able to exist after they have been cut and their 

 connection with the subterranean root system severed. 



Sometimes the aerial roots originating on the stem grow 

 obliquely downwards into the ground and form remarkable 

 stilt-like supports which may be seen in Screw-Pines (Panda- 

 mis), Mangroves (Rhizophora), and, in miniature, sometimes 

 in the Maize (Zea Mays). Some aerial roots possess the excep- 

 tional power of being able to absorb moisture from the air by 

 means of a spongy outer sheath of tissue called the velamen, 

 found in many orchids. In a few cases also the aerial rootF 

 are green m colour and possess chlorophyll. 



